The real culprit is credit card debt, which tends to stifle economic growth of younger Americans, primarily because they pay it off so slowly, the OSU study says. But millennials are paying off all their debts so slowly they may accumulate credit card debt well into their 70s and die still owing, researcher say.

“If what we found continues to hold true, we may have more elderly people with substantial financial problems in the future,” says Lucia Dunn, a lead author of the study and an economics professor at Ohio State.

Perhaps — let’s go out on a limb here and say definitely — that’s a big reason millennials say debt is their “biggest financial concern” of their lives.

That dour sentiment comes from another study, this one from banking giant Wells Fargo, which has 54 percent of millennials saying it’s debt that keeps them up at night.

Another 42 percent of younger Americans say their debt is “overwhelming,” double the percentage of baby boomers who feel the same way. And 51 percent of millennials say they aren’t saving for retirement, primarily because they just don’t have enough extra cash to start a savings program. Any extra cash they do have needs to go to pay down debt, 81 percent of millennials say.

“I am glad to see about half already saving for retirement, but we’re also seeing that half of this generation has not started to save and is putting it off until the 30s,” says Karen Wimbish, director of retail retirement at Wells Fargo. “I can’t stress enough how important it is for this generation to start saving now — the benefits of starting young can’t be recreated later.”

The trouble starts in their early 20s, with ever-skyrocketing student loan debt, Wells Fargo reports. More than 64 percent of millennials funded their college education through loans, compared with 29 percent of baby boomers. The report cites statistics from the Consumer Financial Protection Bureau, which estimates total student loan debt topping $1 trillion last year, far and away the highest figure ever for U.S.-based college loans.

Yet younger Americans aren’t turning to the stock market to grow their financial assets, a potentially big mistake given the historical returns from stocks, which tend to easily best the rate of inflation. About 52 percent of millennials (and 67 percent of younger women) in the Wells Fargo study say they are either “not very confident” or “not at all confident” in the stock market.

“But many are already in the stock market. While it is understandable that this generation is wary, millennials have time on their side and a long runway for future growth,” Wimbish says.

Wells Fargo advises millennials to squeeze more money out of their budget and add it to their 401(k) plans or individual retirement accounts. The good news is that they have time for their retirement savings to grow.

Brian O’Connell has 15 years of experience covering business news and trends, particularly in the financial, health care and career management sectors. He has written 14 books and appeared on CNN, Fox News, CNBC, C-Span, Bloomberg, CBS Radio and other media outlets and in such publications as The Wall Street Journal and The Street.com. He is a former Wall Street bond trader.